***2013 LC Chemistry Before/After***

Laura229

Surely that alone wasnt worth 9 marks though?

lizardspock

There was a pretty bad reaction to the paper from my class, although I thought it was fair enough to be honest. Really hoping I've done enough to secure the A1... Did 10 questions but just kinda found there was a part to most questions which could have the potential to be a bit vague in the marking scheme or parts with just a general sting in them! fingers crossed!

comeclosa

Corrosive for the hazard, yes? :P

SecondMan

comeclosa wrote: »

Corrosive for the hazard, yes? :P

Yes. I drew a hand that resembled a side-view of a rabbit's head.

Hamza Malik

comeclosa wrote: »

Corrosive for the hazard, yes? :P

Yeah I drew the picture of the test tube leaking on to a hand with a dead fish in the background

ladymacbeth

IMG_0671.JPG

Already hitting me that I was wrong.

ladymacbeth

ladymacbeth wrote: »

IMG_0671.JPG

Already hitting me that I was wrong.

Is n1 not = 2 and n2 = 1??

_LilyRose_

ladymacbeth wrote: »

IMG_0671.JPG

Already hitting me that I was wrong.

But isn't the ratio of the iodine to thiosulfate 1:4?

ladymacbeth

Deleted User wrote: »

Is n1 not = 2 and n2 = 1??

:eek:

FUUUUUU*****

Ok. Lesson learned. This is what happens when everything depends on this subject and you're stress levels are at an all time high. This is what happens when you don't read a question properly.

I will remain calm and not shred my exam paper into pieces in frustration. :mad:

_LilyRose_

_LilyRose_ wrote: »

But isn't the ratio of the iodine to thiosulfate 1:4?

Nope.
Iodine to Thiosulfate
1 : 2

Oxygen to Iodine
1 : 2

Therefore
Oxygen to Thiosulfate
1 : 4

_LilyRose_

Deleted User wrote: »

Nope.
Iodine to Thiosulfate
1 : 2

Oxygen to Iodine
1 : 2

Therefore
Oxygen to Thiosulfate
1 : 4

Ah yes.








F************

Laura229

For the ammonia reaction was it wrong to say high pressure and low temperature?

ladymacbeth

_LilyRose_ wrote: »

Ah yes.








F************

hahahaha i'm not alone.
I'm literally so angry I'm laughing it off.
hahahaha... wtf???!!

_LilyRose_

ladymacbeth wrote: »

hahahaha i'm not alone.
I'm literally so angry I'm laughing it off.
hahahaha... wtf???!!

When I looked at my book like two minutes before the exam I had 1:4 highlighted for the winkler calculations I'm soooooo annoyed at myself now lololololol!

Laura229

Laura229 wrote: »

For the ammonia reaction was it wrong to say high pressure and low temperature?

Which question was this?

xJEx

Laura229 wrote: »

For the ammonia reaction was it wrong to say high pressure and low temperature?

I was gonna do that but then I figured it wasnt that since it was a rates not equil. Q ... pus a low temperature increases yield of ammonia but actualy slows down the rate

i said increased concentrations and temperature

xJEx

What answers did people get for Q3? I got .075 moles, then 4.347 for heat change and 57.96 for heat of reaction

ladymacbeth

_LilyRose_ wrote: »

When I looked at my book like two minutes before the exam I had 1:4 highlighted for the winkler calculations I'm soooooo annoyed at myself now lololololol!

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

_LilyRose_

ladymacbeth wrote: »

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

I honestly have no idea! Most people here and that I talked to got different to me but I suppose we'll have to wait to view the papers if we have to haha!

ladymacbeth

ladymacbeth wrote: »

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

I worked with 2:1 for the calculation as we needed the concentration of iodine for the question

Then it asked to work with O2 so I halved the molarity of the iodine. (as 2 moles are liberated for every 1 mole O2)
And then used this figure for the rest of the calculations

Glee_GG

Kingkumar wrote: »

the safety tube wasnt pushed into the water..

Gas I said "the flask appear to be hovering mid-air so you should put a tripod and gauze underneath" :L Its still true though even if I know they would have used it, they didn't put it in the picture!

SecondMan

xJEx wrote: »

I was gonna do that but then I figured it wasnt that since it was a rates not equil. Q ... pus a low temperature increases yield of ammonia but actualy slows down the rate

i said increased concentrations and temperature

Increased pressure would work too as it would cause an increase in collisions.

Kingkumar

Glee_GG wrote: »

Gas I said "the flask appear to be hovering mid-air so you should put a tripod and gauze underneath" :L Its still true though even if I know they would have used it, they didn't put it in the picture!

hahaha i was going to put that as well

xJEx

SecondMan wrote: »

Increased pressure would work too as it would cause an increase in collisions.

Yeah but low temperature wouldn't. It's kind of a messed up question cause temperature would speed it up but it would decrease the yield of ammonia and theyre asking how to speed up the reaction of ''the production of ammonia''

xJEx

xJEx wrote: »

Yeah but low temperature wouldn't. It's kind of a messed up question cause temperature would speed it up but it would decrease the yield of ammonia and theyre asking how to speed up the reaction of ''the production of ammonia''

For production of Ammonia.
By Le Chatalier, the ideal conditions are high pressure and low temperature.
High pressures are expensive to maintain and increase risk of explosion. A compromise pressure of 200 atmospheres is used.
For temperature; if it was too low, the reaction would be too slow and actually slow down production. A compromise temperature of 500 degrees celsius is used.

xJEx

Deleted User wrote: »

For production of Ammonia.
By Le Chatalier, the ideal conditions are high pressure and low temperature.
High pressures are expensive to maintain and increase risk of explosion. A compromise pressure of 200 atmospheres is used.
For temperature; if it was too low, the reaction would be too slow and actually slow down production. A compromise temperature of 500 degrees celsius is used.

Yeah I know but it was a rates question not a equilibrium

xJEx

xJEx wrote: »

Yeah I know but it was a rates question not a equilibrium

Sorry I just saw someone mention ammonia production.

For what speeds up rate of reaction.

1. Nature of reactants (are they both ionic or covalent) didn't apply to question
2. Temperature of reaction
3. Concentration of reactants
4. Particle size didn't apply
5. Presence of a catalyst

0mega

xJEx wrote: »

What answers did people get for Q3? I got .075 moles, then 4.347 for heat change and 57.96 for heat of reaction

Same here but should it have been -57.96 for heat of reaction as it was exothermic and produced heat?

Jackobyte

Glee_GG wrote: »

Gas I said "the flask appear to be hovering mid-air so you should put a tripod and gauze underneath" :L Its still true though even if I know they would have used it, they didn't put it in the picture!

I said they had no water in with their cloves. :P The diagram definitely had more than one flaw so they'll have to be generous with the marking scheme on it.

0mega

0mega wrote: »

Same here but should it have been -57.96 for heat of reaction as it was exothermic and produced heat?

Can I ask how you got the heat change? I had never done a question where the two initial temps were different so I added them both and divided by 2 but I'm guessing that was wrong?

Jackobyte

0mega wrote: »

Same here but should it have been -57.96 for heat of reaction as it was exothermic and produced heat?

Yeah, I made mine negative as well.

@OulDublinHead: Averaging the temps at start was right.

ahmdoda

0mega wrote: »

Same here but should it have been -57.96 for heat of reaction as it was exothermic and produced heat?

flip forgot to include the minus argggggg!!!!!!!!!! hopefully wont loose much dumbass benzoic acid came up so couldnt do q2 so i was forced into 1 and 3

Jackobyte

Jackobyte wrote: »

Yeah, I made mine negative as well.

@OulDublinHead: Averaging the temps at start was right.

Thanks but then the initial temp was 14 and it reached 20.9 so should the heat change not be 6.9? Not around 4?

Glee_GG

Why don't we like air bubbles being trapped in the bottle for Q1?

_LilyRose_

For anyone who did Q8, did ye get UV light, HCl and Cl2 for part (b)? And what did you say for the reaction for conversion X?

simons545

Deleted User wrote: »

Thanks but then the initial temp was 14 and it reached 20.9 so should the heat change not be 6.9? Not around 4?

yep heat change was 6.9

xJEx

ladymacbeth wrote: »

So should it have been 1:4?
Or 2:1 as was suggested in the equation?

2:1 wasn't suggested in the equation for the oxygen??

Glee_GG

Glee_GG wrote: »

Why don't we like air bubbles being trapped in the bottle for Q1?

Because atmospheric O2 will dissolve into the sample and give an unusually high reading for dissolved O2.

_LilyRose_ wrote: »

For anyone who did Q8, did ye get UV light, HCl and Cl2 for part (b)? And what did you say for the reaction for conversion X?

Yup. And it was an ionic addition reaction

xJEx

Deleted User wrote: »

Sorry I just saw someone mention ammonia production.

For what speeds up rate of reaction.

1. Nature of reactants (are they both ionic or covalent) didn't apply to question
2. Temperature of reaction
3. Concentration of reactants
4. Particle size didn't apply
5. Presence of a catalyst

Oh never thought of catayst!! So would it be okay that I said increased temperature speeds up the rate even though it said the reaction was for ''the production of ammonia'' whose yield is decreased by temp?

_LilyRose_

xJEx wrote: »

2:1 wasn't suggested in the equation for the oxygen??

2S2O3 + I2 was written on the paper I think she means

Glee_GG

Deleted User wrote: »

Because atmospheric O2 will dissolve into the sample and give an unusually high reading for dissolved O2.

Ah ok, i had no idea so I just said you'd be adding extra oxygen to the mixture and it would effect results so thats grand out!

_LilyRose_

Deleted User wrote: »

Yup. And it was an ionic addition reaction

Yes! That question 8 terrified me but I made myself do it because I love that organic question!

Jackobyte

Deleted User wrote: »

Thanks but then the initial temp was 14 and it reached 20.9 so should the heat change not be 6.9? Not around 4?

Temperature change is 6.9, which is different to heat change. Heat change is found using:

ΔH=mcΔθ where m is mass, c is heat capacity and Δθ is temp change.

xJEx

xJEx wrote: »

Oh never thought of catayst!! So would it be okay that I said increased temperature speeds up the rate even though it said the reaction was for ''the production of ammonia'' whose yield is decreased by temp?

Yes. A high temperature has to be used to ensure a decent amount of effective collisions. Pressure however would be wrong as pressure affects equilibrium and not rate of reaction.

eoinoc2509

I thought that was horrible! Was i the only one?:(

xJEx

Deleted User wrote: »

Because atmospheric O2 will dissolve into the sample and give an unusually high reading for dissolved O2.

I said since we are calculating dissolved oxygen air bubbles containing oxygen would affect our result.
Would that get me the marks??

xJEx

Jackobyte wrote: »

Yeah, I made mine negative as well.

@OulDublinHead: Averaging the temps at start was right.

Damn i didnt do the negative sign, how many marks would i lose for that?

And so was it 0.075 moles then?

xJEx

xJEx wrote: »

I said since we are calculating dissolved oxygen air bubbles containing oxygen would affect our result.
Would that get me the marks??

If they are being ruthless with the marking scheme, I don't think it will. It all depends on the marking scheme though.

ahmdoda

_LilyRose_ wrote: »

For anyone who did Q8, did ye get UV light, HCl and Cl2 for part (b)? And what did you say for the reaction for conversion X?

i was going to write uv light but i wondered how is uv light a reagent! it would be a condition to carry out the reaction and if that what he wanted the other two answer would of both been nickle catalyst at 200 degree so had cl2 instead

xJEx

Deleted User wrote: »

If they are being ruthless with the marking scheme, I don't think it will. It all depends on the marking scheme though.

But why, what am I leaving out?
i said air contains oxygen so it would affect the ppm result in the end...